Bug of the Week: Arpeggios may collide with laissezVibrer ties

[Graham Percival]

alternate title:
  On the Road to 2.14: let's get this done.

Neil has been steadily working away at regressions, which is
fantastic, but I'm hoping to spur things along.  There 8
code-related Critical issues.  Let's do one each week.  Everybody
jumpes onto the bug.  Make wild suggestions.  Brainstorm.  If you
have an idea but not time to test it, send out an email and hope
that somebody else will do it.  If you have time to test stuff but
no ideas, then start doing a binary search to find the exact
commit the introduced the regression.  Etc.

We'll do this in ascending order, skipping over any issues that
are currently Started or have a patch.


The first such issue is:
http://code.google.com/p/lilypond/issues/detail?id=881
Arpeggios may collide with laissezVibrer ties

We currently have:
- a good code exerpt that demonstrates the bug.
- extensive analysis of the behavior from 2.11.19 (working) to
  2.11.34 (badly broken) from Trevor.
- a few guesses from Neil and Trevor.

Let's get this done!

Cheers,
- Graham


PS.  By "us", I mean "you".  I'm focusing on the other 6 Critical
issues, plus mentoring my two doc editors.